WO2007070060A1

WO2007070060A1 - Heat pump with pulse width modulation control

Info

Publication number: WO2007070060A1
Application number: PCT/US2005/045810
Authority: WO
Inventors: Michael F. Taras; Alexander Lifson
Original assignee: Carrier Corporation
Priority date: 2005-12-16
Filing date: 2005-12-16
Publication date: 2007-06-21
Also published as: EP1996875A4; EP1996875A1; US20080209930A1; CN101341367A

Abstract

A heat pump is provided with a component that has a pulse width modulation control to adjust system capacity. Thus, by utilizing a pulse width modulation technique to control this component, the present invention is able to closely tailor the delivered capacity of the heat pump to that which is demanded, without cycling the unit. In one embodiment, the component has a suction pulse width modulation valve. In another embodiment, the component which is modulated is the compressor pump unit, and, in particular, a pair of scroll members that are allowed to move into and out of contact with each other. The pulse width modulation control device can also be utilized in combination with a heat pump having an economizer function and/or an unloader function.

Description

HEAT PUMP WITH PULSE WIDTH MODULATION CONTROL

BACKGROUND OF THE INVENTION

This invention relates to a heat pump that is operable in both a cooling and a heating mode, and wherein at least one component is controlled by pulse width modulation techniques to vary the capacity of the heat pump.

Refrigerant systems are utilized to control the temperature and humidity of air in various indoor environments to be conditioned. In a typical refrigerant system operating in the cooling mode, a refrigerant is compressed in a compressor and delivered to a condenser (or an outdoor heat exchanger in this case). In the condenser, heat is exchanged between outside ambient air and the refrigerant. From the condenser, the refrigerant passes to an expansion device, at which the refrigerant is expanded to a lower pressure and temperature, and then to an evaporator (or an indoor heat exchanger). In the evaporator, heat is exchanged between the refrigerant and the indoor air, to condition the indoor air. When the refrigerant system is operating, the evaporator cools the air that is being supplied to the indoor environment.

The above description is of a refrigerant system being utilized in the cooling mode of operation. In the heating mode, the refrigerant flow through the system is essentially reversed. The indoor heat exchanger becomes the condenser and releases heat into the environment to be conditioned (heated in this case) and the outdoor heat exchanger serves the purpose of the evaporator and exchanges heat with a relatively cold outdoor air. Heat pumps are known as the systems that can reverse the refrigerant flow through the refrigerant cycle, in order to operate in both heating and cooling modes. This is usually achieved by incorporating a four-way reversing valve (or an equivalent device) into the system design, with the valve located downstream of the compressor discharge port. The four-way reversing valve selectively directs the refrigerant flow through the indoor or outdoor heat exchanger when the system is in the heating or cooling mode of operation, respectively. Furthermore, if the expansion device cannot handle the reversed flow, than, for example, a pair of expansion devices, each along with a check valve, can be employed instead. The operation and control of refrigerant systems faces many challenges. One challenge is that the capacity for either cooling or heating demanded by an environment to be conditioned can vary. It would be desirable to only provide the required capacity, as the energy efficiency and comfort are then improved as the amount of unit cycling is reduced or eliminated. However, heat pumps have typically not been provided with the features assuring sufficient variability as may be desirable, in order to continuously match the required capacity to the capacity delivered by the unit without frequent cycling.

In air conditioning systems, a technique known as a pulse width modulation control has been provided. In this technique, various components are provided with a pulse width modulation control that rapidly cycles the component "on" and "off to change the capacity. As an example, a suction pulse width modulation valve may be rapidly opened and closed to restrict the amount of refrigerant delivered to a compressor. While such pulse width modulation controls provide sufficient performance variability for air conditioning systems, they have not been incorporated into heat pumps to date.

SUMMARY OF THE INVENTION

In a disclosed embodiment of this invention, a four-way reversing valve selectively controls the flow of refrigerant from a compressor discharge to either an outdoor heat exchanger in a cooling mode, or to an indoor heat exchanger in a heating mode. As explained above, the refrigerant flows through a complete cycle under either mode, and returns to the compressor. The refrigerant flow, on its way back to the compressor, once again, passes through the four-way reversing valve. To provide greater variability in capacity delivered by the heat pump system to match external load demands, at least one component within the heat pump system is equipped with a pulse width modulation control. In a disclosed embodiment, this component may be a suction pulse width modulation valve controlling the amount of refrigerant flowing through a suction line to the compressor. In another embodiment, the component which is provided with a pulse width modulation control may be a compressor pump unit. In one disclosed example, in a scroll compressor, a pair of scroll members is selectively held into contact, or allowed to move away from each other in a pulse width modulated manner, thus controlling the amount of refrigerant compressed by the compressor and delivered to other system components.

By utilizing the pulse width modulation control, the present invention is able to tailor the delivered capacity to meet desired capacity requirements for the refrigerant heat pump system. In these arrangements, heat pumps are provided that are better able to match the delivered system capacity and the conditioned environment demanded capacity (and its latent and sensible components) either in the heating or cooling mode of operation.

In other embodiments, an economizer cycle is incorporated into the heat pump schematic to provide additional capacity control. As is known, the economizer cycle essentially taps a portion of the refrigerant flow through an auxiliary expansion device. That portion of the refrigerant flow is passed through an economizer heat exchanger along with the main refrigerant flow. Heat is exchanged between the two refrigerant flows, with the tapped refrigerant cooling the main refrigerant. The tapped refrigerant exits the economizer heat exchanger typically in a vapor state. This vapor is returned to the compressor at some intermediate point in the compression process. The main refrigerant flow passes to a main expansion device and then to a downstream heat exchanger (evaporator), having a greater cooling potential due to additional cooling obtained by passing through the economizer heat exchanger. Various embodiments for configuring and incorporating the economizer cycle in a heat pump system are disclosed in this invention.

The present invention thus allows several additional steps of capacity control. In one embodiment, an unloader function allows for at least a portion of the partially compressed refrigerant to be diverted to the compressor suction to reduce capacity. The several embodiments disclosed in this application thus allow the use of full capacity with pulse width modulation. The control also has access to the unloader function and the economizer function in combination with a modulation of one of the components to further control system capacity.

These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. BRIEF DESCRIPTION QF THE DRAWINGS

Figure IA is a schematic of a first view.

Figure IB shows an alternative method.

Figure 2 shows an alternative schematic.

Figure 3 shows an alternative schematic.

Figure 4 shows an alternative schematic.

Figure 5 shows an alternative for a standard economizer heat exchanger.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Figure IA shows a heat pump refrigerant system 20 incorporating a compressor 22 having a discharge line 23 supplying a compressed refrigerant to a four-way reversing valve 26. The four-way reversing valve 26 selectively communicates the refrigerant from the discharge line 23 either to an outdoor heat exchanger 24, when the system is operating in a cooling mode, or to an indoor heat exchanger 30, when the system is operating in a heating mode. In either case, the refrigerant passes from the heat exchanger it first encounters after leaving the compressor to a main expansion device 28. From the main expansion device 28, the refrigerant passes through to the second heat exchanger, and back to the four-way reversing valve 26. The four-way reversing valve 26 routes the refrigerant into a suction line 31 leading back to the compressor 22. This is a very simplified schematic for a heat pump system. It should be understood that much more complex systems are feasible. A pulse width modulation valve 40 is positioned on the suction line 31. As is known, the pulse width modulation suction valve 40 can be rapidly cycled to control the amount of refrigerant flowing through the compressor. In this manner, the capacity of the refrigerant system can be controlled. As mentioned, such controls are known for use in the air conditioning systems, but have not been utilized in the heat pumps. By incorporating this type of control into the heat pump system, the capacity (and power) of the heat pump in either heating or cooling mode of operation can be precisely tailored to a demanded capacity in a very efficient manner. Typically, cycling times on the order of 3 seconds to 30 seconds are utilized. Figure IB shows an embodiment 301, schematically. It is known that the orbiting scroll member 302 and the non-orbiting scroll member 304 of a scroll compressor may be biased together by means of gas pressure in a chamber 306. Opening and closing the valve 310 can control pressure in the chamber 306. As shown, the valve 310 communicates via a refrigerant line 308 with another pressure source that is at different pressure than pressure in the chamber 306, when the valve 310 is closed. When the pressure in the chamber 306 is reduced below a certain level, the scroll members will separate from each other, and the amount of refrigerant pumped by the compressor is then reduced. When the pressure in the chamber 306 is increased above certain level, the scrolls will come into contact with each other, and then the normal compression process will resume. The valve 310 can be controlled by a pulse width modulation control 312. Thus, by modulating the pressure in the chamber 306, the two scroll members 302 and 304 can be allowed to periodically move away from, and come into contact with, each other. It should be noted that the schematic shown in Figure IB is presented for an illustration purpose only. For example, instead of allowing the scroll 304 to move axially in and out of contact with the scroll 302, the scroll 302 can be allowed to move axially while the scroll 304 remains essentially stationary in the axial direction. Further, the valve 312 can be located internal or external to the compressor. The control 42 (or 312) is operated to provide variation in the amount of refrigerant delivered by the compressor based upon any number of factors. As the capacity demand on the system 20 changes, then the pulse width modulation control can change the amount of refrigerant flowing through the compressor. Moreover, it may well be that less refrigerant would be desirably passed through the compressor in one of the cooling or heating operating modes. Again, the inventive control easily allows such a modification. In addition, as will be discussed below, the unloader bypass feature (if available) provides further variation in the capacity of the entire system, and the ability to better tailor the control to either the heating or cooling modes of operation. Figure 2 shows another embodiment system 100 wherein a second routing valve 102 is positioned to selectively route refrigerant from the heat exchangers 24 and 30 either into a main liquid line 103. Refrigerant flows through the routing valve 102 from either of the heat exchangers 24 or 30 into the liquid line 103. In both heating and cooling modes of operation, the refrigerant passes from the heat exchanger 30 or the heat exchanger 24 to the liquid line 103 initially, through an economizer heat exchanger 104 and then through the main expansion device 28. This refrigerant then flows back through the routing valve 102 downstream to the heat exchanger 24 or the heat exchanger 30 accordingly.

As is known, a tap line 106 selectively taps a portion of the refrigerant from the liquid line 103 and passes that tapped refrigerant to an economizer expansion device 108. This refrigerant flows through the economizer heat exchanger 104 and cools the main refrigerant flow. A vapor injection line 110 returns the tapped refrigerant back to an intermediate compression point in the compressor 22. While the flow of the tapped refrigerant and the main refrigerant flow through the economizer heat exchanger 104 are shown in the same direction, in practice, it is typically preferable that they be in counter-flow relationship. However, for simplicity of illustration, they are shown flowing in the same direction. Also, it has to be noted that the auxiliary expansion device 108 and the economizer flow diversion point can be located downstream of the economizer heat exchanger 104.

As is known, an economizer function allows the provision of increased capacity (and efficiency) by additional cooling of the refrigerant in the main liquid line. Again, the pulse width modulation valve 40 positioned on a suction line 31 may be controlled using pulse width modulation techniques to tailor the provided capacity with the demanded capacity. The economizer feature, along with the optional unloader feature, and the pulse width modulation control, allows the system to operate with minimal amount of cycling to meet particular cooling/heating capacity demands. Figure 3 shows another embodiment, wherein the economizer function is achieved somewhat differently. In the economized cooling mode, tapped refrigerant having passed through a cooling mode economizer expansion device 204 located on a tap line is returned through a vapor injection line 110 to the compressor 22. The refrigerant from the main liquid line passes through a cooling mode economizer heat exchanger 202, the main expansion device 28, and a heating mode economizer heat exchanger 206 to the indoor heat exchanger 30 and back to the compressor 22. Since the tapped refrigerant would not be flowing through the heating mode economizer expansion device 208 in this mode of operation, there is no heat exchanged in the heating mode economizer heat exchanger 206.

When the system 200 operates in the economized heating mode, the refrigerant flow direction throughout the system is essentially reversed, and the tapped refrigerant flows through the heating mode economizer heat exchanger 206 but not through the cooling mode economizer heat exchanger 202. A control controls the economizer expansion devices 204 and 208 such that they also provide a shutoff valve function. When the system 200 is operating in a cooling mode, the expansion device 204 is open and the expansion device 208 is closed. When the system 200 operates in a heating mode, the position of the valves is reversed. Once again, similar to the Figure 2 embodiment, the economizer function along with the suction pulse width modulation valve 40 controlled by the control 42 allows for precise matching of the capacity provided by the heat pump system in either heating or cooling mode of operation to the demanded capacity. Figure 4 shows another embodiment 220 wherein a single economizer heat exchanger 230 is provided. A pair of main expansion devices 224 is provided on each side of the economizer heat exchanger. A bypass line 202 and a check valve 226 are also provided around each main expansion device 224. Now, the refrigerant will pass through one of the selective main expansion devices 224 depending on the mode of operation (cooling or heating) and the refrigerant flow direction, since the flow of the refrigerant around this expansion device will be blocked by the respective check valve 226. At the same time, the refrigerant flow will be allowed around another expansion device but not through it. An economizer expansion device 228 and heat exchanger 230 operate in a manner similar to the Figure 3 embodiment, with the only difference that the economizer flow is tapped either upstream or downstream of the economizer heat exchanger 230. Again, the valve 40 positioned on the suction line 31 and controlled by the control 42 using pulse width modulation techniques, along with the economizer function, allows tailoring the provided capacity to the demanded capacity.

Figure 5 shows an embodiment 260 wherein the economizer heat exchanger is replaced with a flash tank 262. As is known, an inlet line 264 is the main liquid line. It passes into the flash tank 262, where a refrigerant liquid 266 is separated away from a vapor. The vapor is returned through the vapor injection line 268 back to the compressor intermediate port. A return liquid line 270 passes downstream to a heat exchanger or additional expansion device.

In each of the above embodiments, the unloader function may also be incorporated as shown in the Figure 2 embodiment. The present invention thus provides the ability to not only control capacity with an unloader function, and the economizer function, as known. However, the present invention also provides the increased ability to control capacity by operating either the suction pulse width modulation valve 40, or modulating the scroll members by separating them from each other, to control the amount of refrigerant pumped by the compressor (see Figure IB) to further control the delivered capacity. A worker of ordinary skill in the art would recognize when such control over capacity would be desirable. By closely matching the delivered capacity and required capacity either in cooling or heating mode of operation, the invention allows reduction in system "on" and "off cycling and thus enhance its performance and improve comfort in the conditioned space. Normally, the pulse width modulation duty of the refrigerant system component is rapid enough not to cause substantial temperature fluctuations in the conditioned environment. For typical applications, the pulse width modulation cycle is between 3 and 30 seconds.

Although a preferred embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.

Claims

CLAIMSWe claim:

1. A heat pump comprising: a compressor for delivering a compressed refrigerant to a discharge line; a routing flow control device for selectively routing refrigerant from said discharge line to either an outdoor heat exchanger when in a cooling mode of operation, and to an indoor heat exchanger when in a heating mode of operation; and at least one component provided with a pulse width modulation control to control the amount of refrigerant passing through this component.

2. The heat pump as set forth in claim 1, wherein said at least one component is a suction pulse width modulation valve provided on a suction line delivering refrigerant to said compressor.

3. The heat pump as set forth in claim 1, wherein pulse width modulation cycle is between 3 and 30 seconds.

4. The heat pump as set forth in claim 1, wherein said at least one component is a compressor pump unit.

5. The heat pump as set forth in claim 4, wherein said compressor pump unit is modulated by said pulse width modulation control to allow scroll members to move into and out of contact with each other.

6. The heat pump as set forth in claim 1, wherein said heat pump is further provided with an economizer function.

7. The heat pump as set forth in claim 6, wherein said economizer function is provided with an economizer heat exchanger.

8. The heat pump as set forth in claim 6, wherein said economizer function is provided with a flash tank.

9. The heat pump as set forth in claim 1, wherein an unloader function selectively unloads at least a portion of refrigerant at least partially compressed by said compressor back to a suction line.

10. A method of operating a heat pump comprising the steps of:

(1) providing a compressor, said compressor being provided with a discharge line, said discharge line communicating with a flow control device for selectively routing refrigerant from said discharge line to either an indoor heat exchanger in a heating mode of operation, or to an outdoor heat exchanger in a cooling mode of operation;

(2) operating said flow control device to selectively route refrigerant from said discharge line to one of said indoor and outdoor heat exchangers, and to route refrigerant from the other of said indoor and outdoor exchangers back to said compressor; and

(3) selectively operating at least one component in the heat pump with a pulse width modulation control to improve the match between the delivered capacity of the heat pump and a desired capacity.

11. The method as set forth in claim 10, wherein said at least one component is a suction pulse width modulation valve provided on a suction line delivering refrigerant to said compressor.

12. The method as set forth in claim 10, wherein pulse width modulation cycle is between 3 and 30 seconds.

13. The method as set forth in claim 10, wherein said at least one component is a compressor pump unit.

14. The method as set forth in claim 13, wherein said compressor pump unit is modulated by said pulse width modulation control to allow scroll members to move into and out of contact with each other.

15. The method as set forth in claim 10, wherein said heat pump is further provided with an economizer function.

16. The method as set forth in claim 15, wherein said economizer function is provided with an economizer heat exchanger.

17. The method as set forth in claim 15, wherein said economizer function is provided with a flash tank.

18. The method as set forth in claim 10, wherein an unloader function selectively unloads at least a portion of refrigerant at least partially compressed by said compressor back to a suction line.